The FORCES range enables clear and comprehensive learning of STATICS and DYNAMICS covering a variety of theories and topics. An understanding of the way in which forces act and react, is fundamental when studying the application of loads on a variety of fixed structures and rotating machinery. The FORCES form a comprehensive range of equipment, from fixed beams through to rotating machines apparatus, equally suitable for demonstration and experimental work.

## HFC16 Tension Coefficients

The apparatus consists of a jib restrained by two chain ties making a triangulated three dimensional structure. The jib and both ties are fitted with spring balances so that the internal forces can be measured.

## HFC17 Basic Roof Truss

The basic roof truss consists of two rafters or struts and a restraining tie. Both rafters are pivoted at their apex.

The other end of one of the rafters is pivoted to a free standing base, whilst the remaining rafter end runs on ball bearings along a track.

## HFC19 Toggle Joint Apparatus

This apparatus is designed to evaluate forces within a toggle mechanism. Load is applied to the two pairs of links by a hanger suspended from their connecting pivot. One end of the link is pivoted to the base, while the other end is able to move sideways on low friction ball bearing wheels. The moving links are restrained by a horizontal spring balance, which measures the horizontal reaction directly. The angle of the toggle can be varied and adjustment is provided for returning the geometry to its original unloaded state before taking measurements. There are many ways in which the forces can be determined theoretically. The instruction sheet provided with the apparatus takes the opportunity to introduce the use of velocity diagrams to solve essentially static problems by considering virtual motion.

## HFC21 Centrifugal Force Apparatus

This apparatus is used to verify that centrifugal force varies with the square of the speed, the rotating mass, and the radius of gyration. The bench top mounted unit houses a speed-controlled motor, which carries a horizontal boom assembly.

This assembly rotates up to 350rpm and onto which sliding weights are fitted and adjusted. The weights are attached to centrifugal rods, which move outwards during rotation and through crank levers apply a force to an integral load cell. The speed of rotation of the boom is displayed on the front panel along with the centrifugal force reading.

A unique feature is that all three variables can be set and the centrifugal force directly read from the digital force display. Six masses are supplied along with all the necessary tools, spares and accessories. A protective dome covers all rotating parts giving protection to the end user.

## HFC25 Conservation of Angular Momentum

Conservation of linear momentum is well understood and often demonstrated to students. Equally important is the conservation of angular momentum. It is not easy to do meaningful experiments on this, but a highly visual demonstration of almost dramatic impact is the effect of reducing the radius of a rotating mass.

This is often seen in an ice skater performing a pirouette. First they spin round on an axis corresponding to their body, arms outstretched. When they raise their arms above their head, the increase in spin in considerable. Rather than go to an ice rink, students can perform this experiments in the laboratory using the HFC25.

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